Enzyme biosensor based on plasma-polymerized film-covered carbon nanotube layer grown directly on a flat substrate

We report a novel approach to fabrication of an amperometric biosensor with an enzyme, a plasma-polymerized film (PPF), and carbon nanotubes (CNTs). The CNTs were grown directly on an island-patterned Co/Ti/Cr layer on a glass substrate by microwave plasma enhanced chemical vapor deposition. The as-grown CNTs were subsequently treated by nitrogen plasma, which changed the surface from hydrophobic to hydrophilic in order to obtain an electrochemical contact between the CNTs and enzymes. A glucose oxidase (GOx) enzyme was then adsorbed onto the CNT surface and directly treated with acetonitrile plasma to overcoat the GOx layer with a PPF. This fabrication process provides a robust design of CNT-based enzyme biosensor, because of all processes are dry except the procedure for enzyme immobilization. The main novelty of the present methodology lies in the PPF and/or plasma processes. The optimized glucose biosensor revealed a high sensitivity of 38 μA mM^-1 cm^-2, a broad linear dynamic range of 0.25-19 mM (correlation coefficient of 0.994), selectivity toward an interferent (ascorbic acid), and a fast response time of 7 s. The background current was much smaller in magnitude than the current due to 10 mM glucose response. The low limit of detection was 34 μM (S/N = 3). All results strongly suggest that a plasma-polymerized process can provide a new platform for CNT-based biosensor design.